<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
    
        let a = [1,2,3];
        let b = [4,5,6];

        // let c = a.concat(b);
        let c = b.concat(a);

        console.log(a);
        console.log(b);
        console.log(c);

    
    </script>
</body>
</html>